Classify and separate .NET tests for Cloud execution (#823)

* Add Cloud test exclusion metadata

* Classify tests for Cloud execution

* Preserve Cloud connection options in runtime tests

* Run eligible tests against Cloud

* Fix Cloud exclusion analyzer error

* Ignore Cloud test results

* Use double quotes in Cloud test commands

* Rename and document Cloud exclusion reasons

* Remove Cloud exclusion reason descriptions from README

* Derive Cloud exclusion reason names from enum

* Isolate client config tests from process environment

* Separate Nexus registration tests

* Separate hosted Nexus registration test

* Require notes for Cloud test exclusions

* Run Cloud tests in separate job

* Pin checkout action to full SHA

* Classify additional Cloud test exclusions

* Exclude tests that trigger worker shutdown race

* Classify worker client replacement test as local-only